1. Field of Invention
The present invention relates to a driving circuit, and more particularly to a light-emitting diode (LED) driving circuit capable of performing half-cycle or full-cycle detection.
2. Related Art
Light-emitting diodes (LEDs) are small, light, and shock-resistant, and have fine power efficacy, long life, and low cost. Therefore, the LEDs are one of the important elements for backlight sources of liquid crystal displays.
In terms of the operation features, the luminance of an LED varies with the current, so technically, the LED is often driven in the mode that the current remains constant. As the luminance and color of each LED is directly associated with the current flowing through the LED, to realize the best performance of the LEDs, the current must be controlled precisely. Thus, when designing an application device, product developers must consider how to control the current of the LED through a driving circuit and integrated circuits (ICs), so as to control the backlight of the screen.
The patent applicant of the present invention provides an AC/DC converting circuit without a transformer in ROC Patent Publication No. 00533672. The AC/DC converting circuit without a transformer can output a stable constant current, and is applicable to load devices requiring a stable supply current, such as light-emitting elements (for example, LEDs). The technical means of the AC/DC converting circuit without a transformer is using a current switching circuit to limit a load current within a stable scope, in which a control circuit determines an ON/OFF operation of the current switching circuit according to a potential difference between an output and an input of the control circuit. When the potential difference is lower than a predetermined value, the load current is turned on, and when the potential difference is higher than a predetermined value, the load current is turned off. Thus, the load current is effectively limited.
Though the patent described above limits the load current within a stable scope by using a current switching circuit, the backlight performance of a screen may be better if the driving current of the LEDs is more effectively controlled. Therefore, it is a task for researchers to provide a driving circuit capable of precisely controlling the driving current of the LEDs.